I have personally experienced "the shakes" from a pair of aftermarket mirrors on my truck that my insurance company bought and ithe shaking made them functionally worthless. I tried tightening up the connections of the mirror/motor, but nothing helped. I ended up going back to oem quality tow mirrors!!!
The nice thing about the 1A mirrror that the OP just bought is that they SEEM to be of a much higher quality then many other aftermarket ones. And if one has a problem with them, they are backed by decent customer service. Anyway, just my .02...be sure to post back your impressions on quality and function after you get them installed.